1. Field of the Invention
The present invention relates to controlling an optical signal.
2. Brief Description of Related Developments
Tunable laser sources (TLS) for providing a tunable laser signal are known in the art and disclosed e.g. in A. C. Bordinalli, et.al., “High-Performance Phase Locking of Wide Linewidth Semiconductor Lasers by Combined Use of Optical Injection Locking and Optical Phase-Lock Loop”, Journal of Lightwave Technology, Vol. 17, No. 2, 1999, pp. 328–342, B. Cai, et.al., “Microwave frequency synthesis using injection locked laser comb line selection”, Proc. LEOS Summer Topical Meetings, Keystone, 1995, Digest No. 95TH8031, Paper WD2, pp. 13–14, H. Takesue, et.al., “Stable Lightwave Frequency Synthesis Over 1-THz Span Using Fabry-Perot Cavity Containing Polarization-Rotation Elements and Actively Controlled Tunable Bandpass Filter”, IEEE Photonics Technology Letters, Vol. 12, No. 1, 2000, pp. 79–81, Hashimoto et. Al. “Synchronization of subterahertz optical pulse train from PLL-controller colliding pulse modelocked semiconductor laser”, Electronics Letters, Vo. 34, No. 6, 1998, pp. 580–581, John D. Jost et al., “Continuously tunable, precise, single frequency optical signal generator”, Optics Express, Vol. 10, No. 12, 2002, pp. 515–519, Katagiri et.al., “Synchronized pulse-train generation from passively modelocked semiconductor lasers by a phase-locked loop using optical modulation sidebands”, Electronics Letters, Vol. 32, No. 20, 1996, pp. 1892–1894, S.-L. Tsao, et.al., “Phaselocked tunable subcarrier comb generator”, Electronics Letters, Vol. 30, No. 24, 1994, pp. 2059–2060, O. Ishida, “Laser Frequency Synthesis Employing Fibre Four-Wave Mixing”, IEEE Photonics Technologies Letters, Vol. 4, No. 10, 1992, pp. 1171–1173. The disclosure of the aforementioned documents is incorporated herein by reference.